Why is Dracula true to the book, but not Frankenstein?

[Hellstromm, Son of Satan]

I mean, the image we have of Dracula in popular culture is very much how he is depicted in the book. The original Bela Lugosi movie was very true to the book, and most depictions of Dracula are more or less accurate to the source material.

But the image we have of Frankenstein in popular culture is NOT how he is depicted in the original book. The original Boris Karloff movie was nothing like the book, and thus most depictions of Frankenstein don't follow the original book.

Why do you think is that?

Why is Dracula close to the way Bram Stoker imagined him, but Frankenstein is nothing like Mary Shelley imagined him?